Steerable catheter and method for performing medical procedure adjacent pulmonary vein ostia

ABSTRACT

Catheters, systems, and methods are provided for performing medical procedures, such as tissue ablation, adjacent the ostia of anatomical vessels, such as pulmonary veins. The catheter comprises an elongated flexible catheter body including a proximal shaft portion and a distal shaft portion, which has a proximal section pre-shaped to form a curve having an apex sized to be inserted into an anatomical vessel, such as a pulmonary vein, and a distal section configured to contact an ostium of the vessel when the curve apex is inserted within the vessel ostium. The catheter further comprises a steering mechanism configured for decreasing a radius of curvature of the curve.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/678,247, filed on May 5, 2005, and is related to co-pendingU.S. patent application Ser. No. ______ (attorney docket number 05-0203(US02)), filed on the same date, and expressly incorporated herein byreference.

FIELD OF THE INVENTION

The present inventions generally relate to systems and methods fortreating tissue, and more particularly to systems and methods forablating tissue in and around the ostia of vessels, such as pulmonaryveins, and other anatomical openings.

BACKGROUND OF THE INVENTION

Normal sinus rhythm of the heart begins with the sinoatrial node (or “SAnode”) generating an electrical impulse. The impulse usually propagatesuniformly across the right and left atria and the atrial septum to theatrioventricular node (or “AV node”). This propagation causes the atriato contract in an organized manner to transport blood from the atria tothe ventricles, and to provide timed stimulation of the ventricles. TheAV node regulates the propagation delay to the atrioventricular bundle(or “HIS” bundle). This coordination of the electrical activity of theheart causes atrial systole during ventricular diastole. This, in turn,improves the mechanical function of the heart. Atrial fibrillationoccurs when anatomical obstacles in the heart disrupt the normallyuniform propagation of electrical impulses in the atria. Theseanatomical obstacles (called “conduction blocks”) can cause theelectrical impulse to degenerate into several circular wavelets thatcirculate about the obstacles. These wavelets, called “reentrycircuits,” disrupt the normally uniform activation of the left and rightatria.

Because of a loss of atrioventricular synchrony, people who suffer fromatrial fibrillation and flutter also suffer the consequences of impairedhemodynamics and loss of cardiac efficiency. They are also at greaterrisk of stroke and other thromboembolic complications because of loss ofeffective contraction and atrial stasis.

One surgical method of treating atrial fibrillation by interruptingpathways for reentry circuits is the so-called “maze procedure,” whichrelies on a prescribed pattern of incisions to anatomically create aconvoluted path, or maze, for electrical propagation within the left andright atria. The incisions direct the electrical impulse from the SAnode along a specified route through all regions of both atria, causinguniform contraction required for normal atrial transport function. Theincisions finally direct the impulse to the AV node to activate theventricles, restoring normal atrioventricular synchrony. The incisionsare also carefully placed to interrupt the conduction routes of the mostcommon reentry circuits. The maze procedure has been found veryeffective in curing atrial fibrillation. However, not only is the mazeprocedure is technically difficult to do, it also requires open heartsurgery and is very expensive.

Maze-like procedures have also been developed utilizingelectrophysiology procedures, which involves forming lesions on theendocardium (the lesions being 1 to 15 cm in length and of varyingshape) using an ablation catheter to effectively create a maze forelectrical conduction in a predetermined path. The formation of theselesions by soft tissue coagulation (also referred to as “ablation”) canprovide the same therapeutic benefits that the complex incision patternsof the surgical maze procedure presently provides, but without invasive,open heart surgery.

In certain advanced electrophysiology procedures, it is desirable tocreate a lesions around, within, or otherwise adjacent to orifices. Forexample, as part of the treatment for certain categories of atrialfibrillation, it may be desirable to create a curvilinear lesion aroundor within the ostia of the pulmonary veins (PVs), and a linear lesionconnecting one or more of the PVs to the mitral valve annulus.Preferably, such curvilinear lesion is formed as far out from the PVs aspossible to ensure that the conduction blocks associated with the PVsare indeed electrically isolated from the active heart tissue. To dothis, a physician must be able to move the ablation catheter tip along adesired path and either deliver ablative energy while slowly draggingthe tip along the path, or deliver energy at a number of discrete pointsalong that path. Either way, it is crucial that the physician be able toaccurately and controllably move the catheter tip along that path. Whenablating around the PVs, however, energy is typically applied along thecurvilinear path using a free-hand approach, thereby rendering itdifficult to accurately move the catheter tip along that path. Moreimportantly, during the electrophysiology procedure, it is important toprevent inadvertent damage to non-targeted regions, such as the PVsthemselves, which could produce stenosis of the PVs. Thus, it has provendifficult to form circumferential lesions using conventional devices toisolate the PVs and cure ectopic atrial fibrillation.

One technique that has recently been developed to address this problemis disclosed in copending U.S. application Ser. No. 10/983,072, entitled“Preshaped Ablation Catheter for Ablating Pulmonary Vein Ostia withinthe Heart,” which is expressly incorporated herein by reference. In thistechnique, a proximal section of the distal end of the catheter isformed into a curve and inserted into the pulmonary vein, and thenrotated within the pulmonary vein as the ablation catheter tip movesaround the ostium in a predictable arc, thereby ensuring that ablationsare performed along a desired path on the ostium, while also ensuringthat no ablations are performed within the pulmonary vein itself.

While this technique has proven to work fairly well for this intendedpurpose, it has been discovered that the resiliency of the curveincreases the friction between the catheter and the inner surface of thepulmonary vein, thereby causing the curve to grab the inner surface ofthe pulmonary vein and produce a jerking motion as the curve is rotatedwithin the pulmonary vein. In addition, although ablation lesions can beformed in a predictable manner, such technique does not currentlyprovide a means for verifying proper location of the ablation lesions.

Accordingly, in addition to the need of being able to more efficientlyand accurately create circumferential lesions around bodily orifices,such as the ostia of the PVs, there remains a need to be able to allowthe curve of a catheter to be more easily rotated within a vessel, aswell as a need to provide a means for independently verifying thelocation of an operative element, such as an tissue ablation element,relative to the ostium of the vessel.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present inventions, a catheterfor performing a medical procedure on tissue adjacent the ostium of ananatomical vessel, such as a pulmonary vein, is provided. The cathetercomprises an elongated flexible catheter body including a proximal shaftportion and a distal shaft portion, which has a proximal sectionpre-shaped to form a curve having an apex sized to be inserted into ananatomical vessel, such as a pulmonary vein, and a distal sectionconfigured to contact an ostium of the vessel when the curve apex isinserted within the vessel ostium. The catheter further comprises asteering mechanism configured for decreasing a radius of curvature ofthe curve. The curve may be eccentric, in which case, the radius ofcurvature is smallest at the curve apex. By way of non-limiting example,the steering mechanism facilitates rotation of the curve apex within thevessel. In this case, the steering mechanism may simply beuni-directional to effect the decrease in the radius of curvature.

In one embodiment, the distal section is configured to be placed into anon-radial relationship with the vessel ostium when the curve apex isinserted into the vessel ostium. In the case where tissue ablation isdesired, this arrangement allows lesions to be more efficiently formedaround the vessel ostium. To provide better contact between the distalsection and the adjacent tissue, the distal shaft portion may have amedial section pre-shaped to form another curve that bends in adirection opposite to the curve. To effect the afore-describednon-radial relationship between the distal section and the vesselostium, the first curve can be a simple curve, and the other curve acomplex curve that bends in a direction opposite to and out-of-planewith the simple curve.

In accordance with a second aspect of the present inventions, a methodof performing a medical procedure adjacent an ostium of a vessel (e.g.,a pulmonary vein) using the afore-described catheter is provided. Themethod comprises inserting the curve apex into the vessel ostium toplace the distal section in contact with a first tissue site adjacentthe vessel ostium, and placing the proximal section in firm contact withan inner surface of the vessel. In one method, the vessel has a sizethat is smaller than the size of the curve, such that the proximalsection is placed in firm contact with the inner surface of the vesselduring insertion of the proximal section within the vessel ostium. Themethod comprises operating the steering mechanism to decrease the radiusof curvature of the curve within the vessel, whereby the proximalsection is released from firm contact with the inner vessel surface, androtating the decreased curve within the vessel about the curve apex toplace the distal section in contact with a second tissue site adjacentthe vessel ostium. In an optional method, the steering mechanism isoperated to allow the radius of curvature of the curve to increasewithin the vessel, whereby the proximal section is placed in firmcontact with the inner vessel surface again.

In accordance with a third aspect of the present inventions, a method ofperforming a medical procedure on an anatomical vessel (e.g., apulmonary vein) using a catheter having a proximal section and a distalsection is provided. The method comprises forming the proximal sectioninto a curve having an apex. For example, the proximal section may bepre-shaped to form the curve in the absence of an external force. Themethod further comprises inserting the curve apex into the vessel ostiumto place the distal section in contact with a first tissue site adjacentthe vessel ostium. In one preferred method, the vessel ostium has a sizethat is smaller than the size of the curve, such that the proximalsection is placed in firm contact with the inner surface of the vesselduring insertion of the proximal section within the vessel ostium. Themethod further comprises placing the proximal section in firm contactwith an inner surface of the vessel, and decreasing a radius ofcurvature of the curve within the vessel, whereby the proximal sectionis released from firm contact with the inner vessel surface. Forexample, a steering mechanism may be operated to decrease the radius ofcurvature. The method further comprises rotating the decreased curvewithin the vessel about the curve apex to place the distal section incontact with a second tissue site adjacent the vessel ostium. The methodmay optionally comprise operating the steering mechanism to allow theradius of curvature of the curve to increase within the vessel, wherebythe proximal section is placed in firm contact with the inner vesselsurface again.

In one optional method, the distal section is placed into a non-radialrelationship with the vessel ostium when the apex of the curve isinserted into the vessel, so that in the case where tissue ablation isdesired, lesions can be more efficiently formed around the vesselostium. To provide better contact between the distal section and theadjacent tissue, the distal shaft portion may have a medial sectionhaving another proximal section, in which case, the method may furthercomprise forming the other proximal section into another curve thatbends in a direction opposite the first curve. To effect theafore-described non-radial relationship between the distal section andthe vessel ostium, the first curve can be a simple curve, and the othercurve can be a complex curve that bends in a direction opposite to andout-of-plane with the simple curve.

In accordance with a fourth aspect of the present inventions, a methodof performing a medical procedure on an anatomical vessel using acatheter including a catheter body having a proximal section and adistal section, and at least one operative element carried by the distalsection. This method is similar to the afore-described method, with theexception that the operative element(s) is specifically placed in firmcontact with and operated at the first and second tissue sites. By wayof non-limiting example, the operative element(s) may comprise a tissueablative element, in which case, the tissue ablative element may beoperated by delivering ablation energy to the ablative element to createlesions at the respective first and second tissue sites. In anotherexample, the operative element(s) may comprise a tissue mapping element,in which case, the mapping element may be operated by receiving mappingsignals from the mapping element to create mapping data points at thefirst and second tissue sites.

Other features of the present invention will become apparent fromconsideration of the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a plan view of one preferred embodiment of a tissue ablationsystem constructed in accordance with the present inventions;

FIG. 2 is a perspective view of the distal end of an ablation/mappingcatheter used in the tissue ablation system of FIG. 1;

FIG. 3 is another perspective view of the distal end of theablation/mapping catheter of FIG. 2;

FIG. 4 is a plan view of the distal end of the ablation/mapping catheterof FIG. 2;

FIG. 5 is a profile view of the distal end of the ablation/mappingcatheter of FIG. 2;

FIG. 6 is another profile view of the distal end of the ablation/mappingcatheter of FIG. 2;

FIG. 7 is a side view of the distal end of the ablation/mapping catheterof FIG. 2, particularly shown inserted into the ostium of a pulmonaryvein;

FIG. 8 is a front view of the distal end of the ablation/mappingcatheter of FIG. 2, particularly shown inserted into the ostium of apulmonary vein;

FIG. 9 is a front view of the distal end of an alternativeablation/mapping catheter that can be used in the tissue ablation systemof FIG. 2, particularly shown inserted into the ostium of a pulmonaryvein;

FIG. 10 is a cross-sectional view of the ablation/mapping catheter,taken along the line 10-10 of FIG. 1;

FIG. 11 is a cross-sectional view of the ablation/mapping catheter ofFIG. 2, taken along the line 11-11 of FIG. 1;

FIG. 12 is a cross-sectional view of the ablation/mapping catheter ofFIG. 2, taken along the line 12-12 of FIG. 1;

FIG. 13 is a partially cutaway view of the distal end of theablation/mapping catheter of FIG. 2, particularly showing one means forinternally actuating the catheter;

FIG. 14 is a partially cutaway view of the distal end of an alternativeablation/mapping catheter than can be used in the tissue ablation systemof FIG. 1, particularly showing another means for internally actuatingthe catheter;

FIG. 15 is a partially cutaway view of the distal end of anotheralternative ablation/mapping catheter than can be used in the tissueablation system of FIG. 1, particularly showing still another means forinternally actuating the catheter;

FIG. 16 is a front view of monitor displaying graphical representationsof the ablation/mapping catheter of FIGS. 2 and 3, the endocardialsurface of the left atrium of the heart, and a superimposed electricalactivity map; and

FIGS. 17A-17J are plan views of a method of using the tissue treatmentsystem of FIG. 1 to create a circumferential lesion around the ostium ofa pulmonary vein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an exemplary tissue ablation system 2 constructedin accordance with the present inventions is shown. The system 2 may beused within body lumens, chambers or cavities for therapeutic anddiagnostic purposes in those instances where access to interior bodilyregions is obtained through, for example, the vascular system oralimentary canal and without complex invasive surgical procedures. Forexample, the system 2 has application in the diagnosis and treatment ofarrhythmia conditions within the heart. The system 2 also hasapplication in the treatment of ailments of the gastrointestinal tract,prostrate, brain, gall bladder, uterus, and other regions of the body.As an example, the system 2 will be described hereinafter for use inpulmonary veins, and specifically, to electrically isolate one or morearrhythmia causing substrates within the ostium of a pulmonary vein fromthe left atrium of the heart in order to treat ectopic atrialfibrillation.

The medical system 2 generally comprises (1) a ablation/mappingsubsystem 4 for mapping and ablating tissue within the heart; (2) alocalization subsystem 6 for registering mapping data and the movementof a probe within a three-dimensional coordinate system; and (3) agraphical user interface 8 configured for generating and displayinggraphics of the heart and associated anatomical structures, mappingdata, and probe within the three-dimensional coordinate system. Itshould be noted that the elements illustrated in FIG. 1 are functionalin nature, and are not meant to limit the structure that performs thesefunctions in any manner. For example, several of the functional blockscan be embodied in a single device, or one of the functional blocks canbe embodied in multiple devices. Also, the functions can be performed inhardware, software, or firmware.

I. Ablation/Mapping Subsystem

The ablation/mapping subsystem 4 is configured to identify and treat atarget tissue site or sites, e.g., aberrant conductive pathways. To thisend, the ablation/mapping subsystem 4 comprises a conventional guidesheath 12 and an ablation/mapping catheter 14 that can be guided throughthe guide sheath 12. As will be described in further detail below, theablation/mapping catheter 14 is configured to be introduced through thevasculature of the patient, and into the left atrium of the heart, whereit can be used to ablate and map heart tissue within and/or around theostia of selected pulmonary veins. The ablation/mapping subsystem 4 alsocomprises a mapping processor 16 and a source of ablation energy, and inparticular, a radio frequency (RF) generator 18. Although the mappingprocessor 16 and RF generator 18 are shown as discrete components, theycan alternatively be incorporated into a single integrated device.

A. Mapping Processor

The mapping processor 16 is configured to detect, process, and recordelectrical signals within the heart, and specifically, electricalsignals adjacent the ostia of the pulmonary vein. Based on theseelectrical signals, a physician can identify the specific target tissuesites adjacent the pulmonary vein ostia to be ablated, and to ensurethat the arrhythmia causing substrates within the pulmonary vein ostiahave been electrically isolated by the ablative treatment. Such mappingtechniques are well known in the art, and thus for purposes of brevity,will not be described in further detail.

B. RF Generator

The RF generator 18 is configured to deliver ablation energy to theablation/mapping catheter 14 in a controlled manner in order to ablatethe target tissue sites identified by the mapping processor.Alternatively, other types of ablative sources besides the RF generator18 can be used, e.g., a microwave generator, an ultrasound generator, acryoablation generator, and a laser or other optical generator. Ablationof tissue within the heart is well known in the art, and thus forpurposes of brevity, the RF generator 18 will not be described infurther detail. Further details regarding RF generators are provided inU.S. Pat. No. 5,383,874, which is expressly incorporated herein byreference.

C. Guide Sheath

The ablation/mapping catheter 14 may be advanced though the guide sheath12 to the target location. The sheath 12, which should be lubricious toreduce friction during movement of the ablation/mapping catheter 14, maybe advanced over a guidewire in conventional fashion. Alternatively, asteerable sheath may be provided. With respect to materials, theproximal portion of the sheath 12 is preferably a Pebax® material andstainless steel braid composite, and the distal portion is a moreflexible material, such as unbraided Pebax®, for steering purposes. Thesheath 12 should also be stiffer than the ablation/mapping catheter 14.A sheath introducer (not shown), such as those used in combination withbasket catheters, may be used when introducing the ablation/mappingcatheter 14 into the sheath 12. The guide sheath 12 preferably includesa radio-opaque compound, such as barium, so that the guide sheath 12 canbe observed using fluoroscopic or ultrasound imaging, or the like.Alternatively, a radio-opaque marker (not shown) can be placed at thedistal end of the guide sheath 12.

D. Ablation/Mapping Catheter

The ablation/mapping catheter 14 comprises an integrated flexiblecatheter body 20, a plurality of distally mounted operative elements,and in particular, a tissue ablative element 22 and a mapping element24, and a proximally mounted handle 26. The catheter body 20 comprises aproximal member 28 and a distal member 30 that are preferably eitherbonded together at an interface 32 with an overlapping thermal bond oradhesively bonded together end to end over a sleeve in what is referredto as a “butt bond.” Alternatively, the integrated catheter body 20 maynot have separate proximal and distal members 28, 30 that aresubsequently integrated together, but instead, may have an unibodydesign.

The catheter body 20 is preferably about 5 French to 9 French indiameter, with the proximal member 28 being relatively long (e.g., 80 to100 cm), and the distal member 30 relatively short (e.g., 3.5 cm to 10.5cm). As best illustrated in FIG. 10, the proximal member 28 comprises atubular body 34 that is preferably formed from a biocompatiblethermoplastic material, such as a Pebax® material (polyether blockamide) and stainless steel braid composite, which has good torquetransmission properties. In some implementations, an elongate guide coil(not shown) may also be provided within the proximal member 28. As bestillustrated in FIGS. 11 and 12, the distal member 30 comprises a tubularbody 36 that is preferably formed from a softer, more flexiblebiocompatible thermoplastic material such as unbraided Pebax® material,polyethylene, or polyurethane. The distal member 30 preferably includesa radio-opaque compound, such as barium, so that the catheter body 20can be observed using fluoroscopic or ultrasound imaging, or the like.Alternatively, radio-opaque markers (not shown) can be placed along thedistal member 30.

The catheter body 20 has a resilient shape that facilitates thefunctionality of the ablation/mapping catheter 14. In particular, and asis standard with most catheters, the proximal member 28 has anunconstrained straight or linear geometry to facilitate the pushabilityof the ablation/mapping catheter 14 through the guide sheath 12. To thisend, the proximal member 28 further comprises a resilient, straightcenter support 45 positioned inside of and passing through the length ofthe proximal tubular body 34. In the illustrated embodiment, theproximal center support 45 is a circular element formed from resilientinert wire, such as nickel titanium (commercially available under thetrade name nitinol) or 17-7 stainless steel wire. Resilient injectionmolded plastic can also be used. The diameter of the proximal centersupport 45 is preferably between about 0.35 mm to 080 mm.

In contrast, the distal member 30 is configured to be alternately placedbetween a linear geometry (shown in phantom in FIG. 1) and an expandedgeometry. The shape of the distal member 30 is achieved through the useof a center support 46 that is positioned inside of and passes throughthe length of the distal tubular body 36, as illustrated in FIG. 13. Inthe illustrated embodiment, the distal center support 46 is similar tothe proximal center support 45 in composition and dimension. To improvethe torqueability of the distal member 30, which is important to thepredictable and controlled movement of the distal member 30, the distalcenter support 46 is preferably affixed within the distal portion of theproximal member 28 (such as by soldering the proximal end of the distalcenter support 46 to the distal end of the proximal center support 45),so that the torsional force applied to the proximal member 28 istransmitted to the distal member 30 without significant loss.Alternatively, the center supports 45, 46 can be formed of a unibodystructure. To further improve the torqueability of the distal member 30,the proximal end of the center support 46 can be flattened into arectangular cross-sectional geometry, as illustrated in FIG. 11. Inaddition, a filler material, such as epoxy 47, can be injected into theproximal end of the distal tubular body 36 in order to integrate all ofthe internal components of the distal member 30 together to furtherimprove the torqueability at the junction between the proximal anddistal members 28, 30.

Additional details concerning the placement of a center support withinthe distal member of a catheter can be found in U.S. Pat. No. 6,287,301,which is expressly incorporated herein by reference. In alternativeembodiments, a stylet, instead of the center supports 45, 46, can beused. In this case, the stylet can be removably inserted through a lumen(not shown) formed through the catheter body 20 to place the distalmember 30 into its expanded geometry.

As best shown in FIGS. 2 and 3, the distal member 30 has fourgeometrically distinct sections: (1) a shaft transition section 38 thatdistally extends from the proximal member 28; (2) a proximal section 40that distally extends from the shaft transition section 38 and serves toprovide an anchoring point within the vessel ostium around which theablative/mapping elements 22, 24 can be positioned; (3) a medial section42 that distally extends from the proximal section 40 and serves toproperly locate the distal section 44 relative to the tissue outside ofthe vessel ostium; and (4) a distal section 44 that distally extendsfrom the medial section 42 and serves to carry the ablative element 22.The distal member 30 is uniquely shaped to perform the aforementionedfunctions.

In particular, referring further to FIGS. 2-6, the shaft transitionsection 38 is pre-shaped into a straight geometry. In the illustratedembodiment, the proximal member 28 and transition section 38 of thedistal member 30 are collinear (i.e., the proximal member 28 andtransition section 38 are not angled relative to each other). In thismanner, bending forces that would otherwise be applied at the interface32 between the proximal and distal members 28, 30 are minimized, therebyallowing more axial force to be applied to the ablation/mapping catheter12 without collapsing the distal member 30 onto the proximal member 28when proximal resistance is applied to the distal member 30. Suchproximal resistance would typically be encountered within placing thedistal member 30 within the ostium of a vessel, as will be described infurther detail below.

As best illustrated in FIG. 4, the proximal section 40 is configured tobe internally actuated from a straight geometry to form a simple curveC1 (i.e., a curve that lies in a single plane, and in this case, planeP1 as illustrated in FIG. 5) in the absence of an external force (e.g.,the force of gravity and the compressive force otherwise applied to thedistal member 30 by the guide sheath 14). In the embodiment illustratedin FIG. 1, internal actuation of the proximal section 40 is accomplishedby pre-shaping the proximal section 40 into the desired curve, and inparticular, by incorporating the pre-shaped center support 46 into thedistal member 30, as discussed above. The particular unconstrained shapeof the proximal section 40 is such that an apex A1 of the simple curveC1 can be conveniently inserted into the ostium O of an anatomicalvessel V, as illustrated in FIGS. 7 and 8. Preferably, to facilitatethis insertion, the simple curve C1 bends more than 70 degrees,preferably more than 90 degrees, and more preferably, greater than 135degrees. However, the bend of the simple curve C1 is preferably not sogreat that the proximal section 40 does not intersect itself.

The medial section 42 is configured to be internally actuated from astraight geometry to form a complex curve (i.e., a curve that can beprojected onto more than one plane) in the absence of an external force,and in particular, a compressive force. In the embodiment illustrated inFIG. 1, internal actuation of the medial section 42 is accomplished bypre-shaping the medial section 42 into the desired curve, as will bedescribed in further detail below. The particular unconstrained shape ofthe medial section 42, is such, that it bends opposite to andout-of-plane with the simple curve C1. That is, the complex curve has aproximal curve C2 that, when projected onto the plane P1 (see FIG. 4),bends opposite to the simple curve C1, and a distal curve C3 that, whenprojected on a plane P2 that is perpendicular to the longitudinal axis Lof the proximal member 28 (see FIG. 6), bends out of the plane P1. Aswill be described in further detail below, the proximal projected curveC2 serves to properly locate the distal section 44 into contact with thetissue located outside of the vessel ostium O, as illustrated in FIG. 7.The distal projected curve C3 serves to place the distal section 44 intoa non-radial relationship (i.e., oblique or tangential) with the vesselostium O, as illustrated in FIG. 8.

In the illustrated embodiment, the proximal projected curve C2 has a 90degree bend, so that the distal section 44 can be placed firmly againstthe tissue surrounding the vessel ostium O, as illustrated in FIG. 7.Alternatively, the proximal projected curve C2 can have a greater than90 degree bend to maximize the contact between the distal section 44 andthe surrounding tissue, but preferably does not exceed 135 degrees tominimize any chance that the distal section 44 may enter into the vesselostium O. In the illustrated embodiment, the distal projected curve C3has a 90 degree bend, so that the distal section 44 is arrangedtangentially relative to the vessel ostium O, as illustrated in FIG. 8.Alternatively, the distal projected curve C3 may have any bend thatarranges the distal section 44 obliquely relative to the vessel ostium,but preferably falls within the range of 60 to 120 degrees, so that theoblique relationship of the distal section 44 falls within the range of−30 to 30 degrees from the tangent. In this manner, the distal section44 spans as much of the tissue surrounding the vessel ostium O aspossible.

As best illustrated in FIGS. 5 and 6, the distal section 44 ispre-shaped into a straight geometry. Alternatively, the distal section44 may be pre-shaped into a curved geometry. In this case, the distalsection 44 preferably forms a simple curve C4 having an apex A2 thatpoints away from the longitudinal axis L1 of the proximal member 28, asillustrated in FIG. 9. In this manner, the shape of the distal section44 will conform better with the perimeter of the vessel ostium O.Notably, such a configuration will form the ablative element 22 into acurvilinear ablative element (as opposed to a linear ablative elementthat would be formed when mounted on a catheter section that isstraight).

Alternatively, rather than pre-shaping the proximal section 40 of thedistal member 30, a steering mechanism may be used to bend the proximalsection 40. In particular, FIG. 14 illustrates an ablation/mappingcatheter 112 that is similar to the previously described catheter 12,with the exception that a steering mechanism is used to transform theproximal section 40 of the distal member 28 from its straight geometryinto its curved geometry, as illustrated in FIG. 14. In particular, thecatheter 112 comprises a steering mechanism 114 that is incorporatedinto the handle 26, and a steering wire 116 with its proximal endattached to the steering mechanism 114 and its distal end connected tothe center support 46 at the interface between the proximal and medialsections 40, 42 of the distal member 30. The steering wire 116 isattached to the side of the center support 46 that faces the directionin which the proximal section 40 of the distal member 30 is configuredto curve or bend (as shown in phantom).

Alternatively, as illustrated in FIG. 15, a center support 118 thatterminates at the interface between the proximal and medial sections 40,42 of the distal member 30 can be used, in which case, a resilient wire120, which is suitably mounted to the distal end of the center support46, can be used to pre-shape the intermediate/distal sections 42, 44, asdescribed above. In this case, the center support 46 can be designed toprovide the catheter 112 with steering capability independent of thedesign constraints imposed by pre-shaping the intermediate/distalsections 42, 44.

In any event, the steering mechanism 114 comprises a rotatable steeringlever 122, which when rotated in one direction, tensions the steeringwire 116, thereby flexing the center support 46, and thus the proximalsection 40 of the distal member 30, into the desired curve (shown inphantom). In contrast, rotation of the steering lever 122 in theopposite direction provides slack in the steering wire 116, therebyallowing the resiliency of the center support 46 to flex the proximalsection 40 of the distal member 30 back into a straight geometry.Alternatively, the steering lever may be of the sliding type, whereinrearward movement of the steering lever flexes the center support 46,and thus the proximal section 40 of the distal member 30, into thedesired curve, and forward movement of the steering lever allows theresiliency of the center support 46 to flex the proximal section 40 ofthe distal member 30 back into the straight geometry. Steeringmechanisms for bending the distal ends of the catheters are well knownin the prior art, and thus need not be described in further detail.

It should be appreciated that the use of a steering mechanism has theadded advantage of providing a means for optionally reducing the radiusof curvature of the simple curve C1 to facilitate its rotation withinthe pulmonary vein, as will be described in further detail below. In anoptional embodiment, the proximal section 40 is both pre-shaped anddeflected using a steering mechanism. This is particularly advantageousin that the rigidity and torqueability of the distal member 30 need notbe decreased to facilitate full bending of the proximal section 40 bythe steering mechanism. That is, typically, in a catheter where only asteering mechanism is used to deflect the catheter, the distal catheterend must be made as flexible as possible in order to achieve the desiredbend within the catheter. However, because, in the optional embodiment,the proximal section 40 is pre-shaped to form the desired bend (i.e.,the simple C1), the distal member 30 can be relatively stiff, therebyproviding for better control of the distal member 30, and allowing thenatural resiliency of the distal member 30 to facilitate anchoring ofthe proximal section 40 within the pulmonary vein. The addition of thesteering mechanism provides the added benefit of optionally decreasingthe radius of curvature of the simple curve C1 as briefly discussedabove, and which will be described in further detail below.

As briefly discussed above with respect to FIG. 1, the ablation/mappingcatheter 12 comprises a tissue ablative element 22, which is mounted onthe distal member 30 of the catheter body 20. In the illustratedembodiment, the ablative element 22 takes the form of a linear electrodeassembly that includes a cap electrode 48 mounted to the distal tip ofthe distal member 30 and a ring electrode 50 mounted on the distalsection 44 of the distal member 30 just proximal to the cap electrode48.

Notably, the split nature of the ablative element 22 provides selectivemonopolar and bipolar functionality to the catheter 12. That is, one orboth of the tip/ring electrodes 48, 50 can be configured as one pole ofa monopolar arrangement, so that ablation energy emitted by one or bothof the electrodes 48, 50 is returned through an indifferent patchelectrode (not shown) externally attached to the skin of the patient; orthe tip/ring electrodes 48, 50 can be configured as two poles of abipolar arrangement, in which energy emitted by one of the tip/ringelectrodes 48, 50 is returned to the other electrode. In addition toserving as a selective unipolar/bipolar means of ablation, the tip/ringelectrodes 48, 50 may also serve as a closely spaced high resolutionpair of mapping electrodes. The combined length of the ablationelectrodes 48, 50 is preferably about 6 mm to about 10 mm in length. Inone embodiment, each ablation electrode is about 4 mm in length with 0.5mm to 3.0 mm spacing, which will result in the creation of continuouslesion patterns in tissue when coagulation energy is appliedsimultaneously to the electrodes 48, 50.

The ablation electrodes 48, 50 may take the form of solid rings ofconductive material, like platinum, or can comprise a conductivematerial, like platinum-iridium or gold, coated upon the device usingconventional coating techniques or an ion beam assisted deposition(IBAD) process. For better adherence, an undercoating of nickel ortitanium can be applied. Any combination of the electrodes can also bein the form of helical ribbons or formed with a conductive ink compoundthat is pad printed onto a nonconductive tubular body. A preferredconductive ink compound is a silver-based flexible adhesive conductiveink (polyurethane binder), however other metal-based adhesive conductiveinks such as platinum-based, gold-based, copper-based, etc., may also beused to form electrodes. Such inks are more flexible than epoxy-basedinks.

The ablation electrodes 48, 50 can alternatively comprise a porousmaterial coating, which transmits coagulation energy through anelectrified ionic medium. For example, as disclosed in U.S. Pat. No.5,991,650, ablation electrodes may be coated with regenerated cellulose,hydrogel or plastic having electrically conductive components. Withrespect to regenerated cellulose, the coating acts as a mechanicalbarrier between the surgical device components, such as electrodes,preventing ingress of blood cells, infectious agents, such as virusesand bacteria, and large biological molecules such as proteins, whileproviding electrical contact to the human body. The regeneratedcellulose coating also acts as a biocompatible barrier between thedevice components and the human body, whereby the components can now bemade from materials that are somewhat toxic (such as silver or copper).

The ablation electrodes 48, 50 are electrically coupled to individualwires 52 (shown in FIGS. 10-12) to conduct ablation energy to them. Thewires 52 are passed in conventional fashion through a lumen extendingthrough the associated catheter body, where they are electricallycoupled either directly to a connector (not shown) that is received in aport on the handle 26 or indirectly to the connector via a PC board (notshown) in the handle 26. The connector plugs into the RF generator 18(shown in FIG. 1). Although ablation electrodes 48, 50 have beendescribed as the operative elements that create the lesion, otheroperative elements, such as elements for chemical ablation, laserarrays, ultrasonic transducers, microwave electrodes, and ohmicallyheated hot wires, and such devices may be substituted for the electrodes48, 50.

The ablation/mapping catheter 14 further comprises temperature sensors(not shown), such as thermocouples or thermistors, which may be locatedon, under, abutting the longitudinal end edges of, or in between, theelectrodes 48, 50. In some embodiments, a reference thermocouple (notshown) may also be provided. For temperature control purposes, signalsfrom the temperature sensors are transmitted to the RF generator 18 byway of wires (not shown) that are also connected to the aforementionedPC board in the handle 26. Suitable temperature sensors and controllers,which control power to electrodes based on a sensed temperature, aredisclosed in U.S. Pat. Nos. 5,456,682, 5,582,609 and 5,755,715.

In the illustrated embodiment, the mapping element 24 takes the form ofa pair of ring electrodes 52, 54 that are mounted on the medial section42 of the distal member 30. Optionally, additional pairs of ringelectrodes may be located along the distal member 30. The mappingelectrodes 52, 54 are composed of a solid, electrically conductingmaterial, like platinum or gold, attached about the catheter body 20.Alternatively, the mapping electrodes 52, 54 can be formed by coatingthe exterior surface of the catheter body 20 with an electricallyconducting material, like platinum or gold. The coating can be appliedusing sputtering, ion beam deposition, or equivalent techniques. Themapping electrodes 52, 54 can have suitable lengths, such as between 0.5and 5 mm. In use, the mapping electrodes 52, 54 sense electrical eventsin myocardial tissue for the creation of electrograms, and areelectrically coupled to the mapping processor 16 (shown in FIG. 1). Asignal wire 54 (shown in FIGS. 10-12) is electrically coupled to eachmapping electrode 52, 54. The wires 54 extend through the catheter body20 into an external multiple pin connector (not shown) located on thehandle 26, which electrically couples the mapping electrodes 52, 54 tothe mapping processor 16.

II. Localization Subsystem

Referring back to FIG. 1, the localization subsystem 6 includes aplurality of tracking elements 56, a plurality of reference elements 58,and a controller/processor 60 coupled to the reference elements 58 andtracking elements 56. As shown in the ablation/mapping subsystem 4illustrated in FIG. 1, the tracking elements 56 (in this case, aproximal element 56(1), a medial element 56(2), and a distal element56(3)) are carried by the distal member 30 of the mapping/ablationcatheter 14. Significantly, the proximal tracking element 56(1) islocated at the proximal end of the proximal section 40, the medialtracking element 56(2) is located at the proximal end of the medialsection 42, and the distal tracking element 56(3) is located at theproximal end of the distal section 44, as illustrated in FIGS. 2 and 3.

At least some of the reference elements 58 are carried by a pair ofreference catheters (not shown). The distal end of each referencecatheter may optionally comprise a plurality of electrodes (not shown),e.g., to provide the reference catheter with mapping functionality. Thereference catheters may be affixed within selected regions of the heart,in order to establish an internal three-dimensional coordinate system,as will be further discussed below. Alternatively, the referenceelements 58 may be located outside of the patient's body, e.g., affixedto the patient's skin, in order to establish an externalthree-dimensional coordinate system.

In any event, the controller/processor 60 can establish athree-dimensional coordinate system by controlling and processingsignals transmitted between the spaced apart reference elements 58. Inessence, the three-dimensional coordinate system provides an absoluteframework in which all spatial measurements will be taken. Thecontroller/processor 60 can also determine the positional coordinates ofthe tracking elements 56, and thus the distal end of themapping/ablation catheter 14, within this coordinate system. As will bedescribed in further detail below, this positional information canultimately be used to graphically reconstruct a chamber of the heart, aswell as the valves and vessel ostia of the heart. The positionalinformation will also ultimately be used to graphically reconstruct thedistal end of the mapping/ablation catheter 14 (as well as any referencecatheters), track the movement of the mapping/ablation catheter 14within the heart chamber, heart valves, and vessel ostia, and, inconjunction with the mapping data obtained from the mapping processor16, generate an electrophysiological map.

In the illustrated embodiment, the localization subsystem 6 employsultrasound triangulation principles to determine the coordinates of thetracking elements 56 carried by the mapping/ablation catheter 14. Inthis case, the location and reference elements 56, 58 take the form ofultrasound transducers. The coordinates of the tracking elements 56 canbe determined within an internal reference frame established byarranging the reference elements 58 in three-dimensional space. Forexample, the first two dimensions of the coordinate system can beprovided by placing a reference catheter within the coronary sinus (CS)(not shown) of the heart, thereby disposing its reference elements 58 ina two-dimensional plane. The third dimension can be provided by placinganother reference catheter within the right ventricular (RV) apex (notshown) of the heart to dispose its reference elements 58 off of thetwo-dimensional plane. Notably, only four reference elements 58 areneeded to provide the three dimensions. Any remaining reference elements58 can be used to improve the accuracy of the triangulation process.

The controller/processor 60 is operated to sequentially transmitultrasound pulses (e.g., 500 KHz pulses) through each reference element58, and then measure the time delay between the respective transmit andreceive pulses at the tracking element 56 and other reference elements58. The controller/processor 60 then calculates the relative distancesbetween each reference element 58 and the remaining reference elements58 and tracking elements 56 using the “time of flight” and velocity ofthe ultrasound pulses. The distance information can be calculated asd=vt, where d is the distance between the transmitter and receiver, v isthe velocity of the ultrasound signal within the medium (i.e., blood),and t is the time delay. To simplify the distance computations, thevelocity of the ultrasound pulses may be assumed to be constant. Thisassumption typically only produces a small error when the referenceelements 58 are located inside the body, since the velocity ofultrasound propagation is approximately the same in body tissue andblood.

The controller/processor 60 then establishes a three-dimensionalcoordinate system by triangulating the distances between the referenceelements 58, and determines the positions of each of the trackingelements 56 within that coordinate system by triangulating the distancesbetween the reference elements 58 and the tracking elements 56.Additional details on determining the positions of ultrasoundtransducers within a three-dimensional coordinate system can be found inU.S. Pat. No. 6,490,474 and U.S. patent application Ser. No. 09/128,304,entitled “A dynamically alterable three-dimensional graphical model of abody region,” which are fully and expressly incorporated herein byreference.

It should be noted that there are other means for determining thepositions of catheters within a three-dimensional coordinate system. Forexample, magnetic tracking techniques, such as that disclosed in U.S.Pat. No. 5,391,199, which is expressly incorporated herein by reference,can be employed. As another example, a voltage tracking technique, suchas that disclosed in U.S. Pat. No. 5,983,126, which is expresslyincorporated herein by reference, can be employed.

III. Graphical User Interface

Referring still to FIG. 1, the graphical user interface 8 comprises agraphical processor 62, a user input device 64, and an output device 66(and specifically, a monitor). The graphical processor 62 is configuredfor generating a representation of the surface of an internal anatomicalstructure (in this case, the endocardial surface within the left atriumof the heart, including the ostium O of selected pulmonary veins) in theform of a computer-generated graphical representation S, which is thendisplayed in a 3-D display window 72 on the monitor 66, as illustratedin FIG. 16. The three-dimensional graphical processor 62 accomplishesthis by acquiring the positions of the tracking elements 56 within theglobal coordinate system from the localization subsystem 6 as themapping/ablation catheter 14 is moved around within the cavity of theleft atrium, including the ostia of the pulmonary veins, and thendeforming the surface representation S (in particular, an anatomicalshell) to the position of the distal tip of the catheter 14, which isextrapolated from the acquired positions of the tracking elements 56 andthe known geometry of the catheter 14.

As will be described in further detail below, the surface representationS can be initially deformed to include interior points (i.e., pointsperiodically acquired, e.g., once every heart, while the catheter 14 ismoved around in the left atrium) and subsequently refined to includesurface points (i.e., points taken at designated times when the distalcatheter tip is touching the endocardial surface of the left atrium).Although only the endocardial surface within the left atrium is shownreconstructed in FIG. 16, it should be noted that the other chambers(right atrium and left and right ventricles) of the heart can begraphically reconstructed in the same manner by moving the distal end ofthe catheter 14 within the respective chambers to acquire interior andsurface points.

In addition to generating graphical representations of anatomicalstructures, the graphical processor 62 is also configured for generatinga graphical representation C of the mapping/ablation catheter 14 withinthe established coordinate system, which is then superimposed over thegraphical heart representation S in the 3D display window 72, asillustrated in FIG. 16. The graphical processor 62 can generate thegraphical catheter model C from a pre-stored graphical model of thecatheter 14, which can be deformed in accordance with the calculatedpositional coordinates of the tracking elements 56 carried by thecatheter 14. In the illustrated embodiment, the graphical catheterrepresentation C is dynamically generated in real-time. That is, thecatheter representation C is graphically generated in successive timeperiods (e.g., once every heartbeat), so that it moves and bends as theactual catheter 14 is moved and bent within the heart chamber. Thegraphical processor 62 may optionally be configured to generategraphical representations of the reference catheters (not shown) inreal-time.

The graphical processor 62 is also configured for generating anelectrical activity map EP within the established coordinate system,which is then superimposed over the graphical heart representation S inthe 3D display window 72, as illustrated in FIG. 16. The graphicalprocessor 62 can generate the electrical activity map EP based on theelectrical activity information acquired from the ablation/mappingsubsystem 4 and the positions of the mapping electrodes 24 geometricallyderived from the positions of the tracking elements 56 obtained from thelocalization subsystem 6. This electrical activity map illustrates sitesof interest, e.g., electrophysiology recording and ablation sites, forproviding subsequent ablative treatment, and can be provided in the formof an isochronal or isopotential map. The electrical activityinformation may also be displayed separately from the 3D display window72.

Additional details on graphically generating heart chambers, catheters,and electrical activity maps within a three-dimensional environment canbe found in U.S. Pat. No. 6,490,474 and U.S. patent application Ser. No.09/128,304, entitled “A dynamically alterable three-dimensionalgraphical model of a body region,” which have previously beenincorporated herein by reference.

The user input device 64 allows the user to interact with the graphicsdisplayed on the monitor 66, and comprises a standard keyboard 68 and agraphical pointing device 70, such as a mouse. The graphical processor62 responds to the user input device 64 by manipulating the graphicswithin the 3D display window 72. As an example, the user may rotate the3D display window 72 in three-dimensions and “zoom” towards or away fromthe window 72 by clicking on the appropriate icon in the manipulationbox 74 using the mouse 70. The user may also select one of the standardorientations, used in fluoroscopy, such as anterior-posterior (AP),lateral, right anterior oblique (RAO) or left anterior oblique (LAO) byselecting the appropriate icon in orientation box 76 using the mouse 70.The user may also select which catheters to display in real-time bychecking the appropriate icons in the real-time box 78 using the mouse70.

Using the mouse 70, the user can also mark anatomical regions ofinterest on the heart model by placing a cursor 84 at the appropriatelocation on the surface representation S and clicking. In theillustrated embodiment, the user can either mark the endocardial surfacerepresentation S with point markings PM or with line markings LM (eitherlinear or curvilinear). For example, if the user desires to place apoint marking PM at an anatomical region of interest, the appropriateicon in the marking box 80 can be clicked, and then the user can markthe surface representation S by moving the cursor 84 to a selectedregion on the surface representation S and clicking the mouse 70. Thesurface representation S can be marked with additional point markings PMin the same manner. If the user desires to place a line marking LM at ananatomical region of interest, the appropriate icon in the marking box80 can be clicked, and then the user can mark the surface representationS by clicking the mouse 70, and dragging the cursor 84. If curvilinear,the line marking LM may either be open or closed. The user may alsoerase marks PM/LM from the surface representation S by clicking on theappropriate icon in the marking box 80, and them moving the cursor 84over the mark PM/LM, while clicking the mouse 70. Point/line markingsPM/LM can also be automatically marked on the surface representation Seach time ablation energy is delivered to the ablation electrodes 48,50, thereby allowing the user to automatically keep track of thelesions. For example, a point marking PM can be created when a discretelesion is created, and a line marking LM can be created when acontinuous line lesion is created.

The user may also select whether the graphical processor 62 performs“passive chamber deformation,” which deforms the surface representationS outward to include outerlying interior points acquired by the catheter14 over successive time periods (e.g., every heart beat) or “snapdeformation,” which deforms the anatomical shell to a surface pointacquired by the catheter 14 (preferably, somewhere on the endocardialsurface) when designated by the user. The user may click the “PassiveDeformation” icon in the deformation box 82 using the mouse 70 to promptthe graphical processor 62 to perform passive chamber deformation as thedistal end of the catheter 14 is moved within the left atrium of theheart, or may click the “Snap Deformation” icon in the deformation box82 using the mouse 70 to prompt the graphical processor 62 to performsnap deformation each time the distal catheter tip is placed intocontact with the endocardial surface of the left atrium.

Having described the structure of the treatment system 2, its operationin creating a circumferential lesion within the ostium O of a pulmonaryvein PV, thereby electrically isolating arrhythmia causing substrateswithin the pulmonary vein PV from the left atrium LA of the heart H,will now be described with reference to FIGS. 17A-17J. It should benoted that the views of the heart H and other interior regions of thebody described herein are not intended to be anatomically accurate inevery detail. The figures show anatomic details in diagrammatic form asnecessary to show the features of the embodiment described herein.

First, under fluoroscopy, the reference catheters are intravenouslyintroduced into the heart, and in particular, within the coronary sinus(CS) and right ventricle (RV) apex, so that the reference elements 58are fixed within a three-dimensional arrangement (reference cathetersnot shown). The guide sheath 12, or another guide sheath, can be used tointroduce the reference catheters into the desired locations of theheart. During introduction of the reference catheters, the localizationsubsystem 6 may be operated to transmit signals between the referenceelements 58, so that the locations of the distal ends of the referencecatheters can be determined and graphically displayed in the 3D displaywindow 72 on the monitor 66.

Next, the guide sheath 12 is introduced into the left atrium LA of theheart H (FIG. 17A). Introduction of the guide sheath 12 within the leftatrium LA can be accomplished using a conventional vascular introducerretrograde through the aortic and mitral valves, or can use a transeptalapproach from the right atrium, as illustrated in FIG. 17A. A guidecatheter or guide wire (not shown) may be used in association with theguide sheath 12 to aid in directing the guide sheath 12 through theappropriate artery toward the heart H. Of course, the guide sheath 12can be introduced into other chambers of the heart H, such as the leftventricle, e.g., if the disease to be treated is ventriculartachycardia.

Once the distal end of the guide sheath 12 is properly placed, theablation/mapping catheter 14 is introduced through the guide sheath 12until the distal member 30 is deployed from the guide sheath 12 (FIG.17B). As can be seen, the curvable section of the catheter body 20, andin particular the proximal section 40, is automatically placed into itscurved geometry (i.e., it forms the curve C1 with the apex A1) due toits pre-shaped nature. Alternatively, if the catheter 12 is steerable,the steering mechanism can be manipulated to subsequently place theproximal section 40 into its curved geometry when desired. In any event,during the introduction of the catheter 14, the localization subsystem 6may be operated to transmit signals between the reference elements 58and the tracking elements 54, so that the locations of the distal end ofthe catheter 14 can be determined and graphically displayed in the 3Ddisplay window 72.

The graphical processor 62 is then operated in the “Passive Deformation”mode, and the catheter 14 is moved around within the left atrium LA asthe position of the distal catheter tip is determined. As a result, thegraphical processor 62 generates the surface representation S (shown inFIG. 16), which begins as a generally spherical shape, and deforms it toinclude the interior anatomical points that are acquired by the catheter14 outside of the endocardial surface representation S (shown in FIG.16). The graphical processor 62 can then be operated in the “SnapDeformation” mode to refine the surface representation S, in which case,the distal tip of the catheter 14 will be placed against selectedregions of the endocardial surface, so that the graphical processor 62can deform the surface representation S to the surface points acquiredby the distal catheter tip. During its deformation in both PassiveDeformation and Snap Deformation modes, the surface representation S isdisplayed in the 3D display window 72 on the monitor 66. Alternatively,rather than use the catheter 14 to acquire points for graphicallygenerating the representation S, a separate catheter having the samelocalization capabilities as the catheter 14 can be used to acquire thepoints.

Next, the catheter 12 is retracted into the sheath 12, and the distalend of the sheath 12 is placed adjacent a selected pulmonary vein PV(FIG. 17C). Once the guide sheath 12 is properly placed, the distalmember 30 of the catheter 14 is deployed from the guide sheath 12 (FIG.17D). The apex A1 of the curve C1 is then inserted into the ostium O ofthe pulmonary vein PV until the intermediate/distal sections 42, 44, andin particular, the ablative element 22 and mapping element 24, areplaced into contact with tissue sites adjacent the ostium O (FIGS. 17E-1and 17E-2). As can be seen, the curve C2 of the medial section 42directs the distal section 44 towards the tissue outside of the ostiumO, and the curve C3 of the medial section 42 places the distal section44 in a non-radial relationship, and specifically a tangentialrelationship, with the ostium O.

Notably, the resiliency of the medial section 42 of the distal member 30places the ablative/mapping elements 22, 24 in firm and stable contactwith the tissue sites. Also, because the distal member 30 comprises aradio-opaque substance, the relative locations of the portions of theproximal section 40 on either side of the apex A1 will provide theoperator with an indication of the extent to which the curve C1 isplaced within the pulmonary vein O, and thus, an indication of thelocation of the ablative/mapping elements 22, 24 relative to the ostiumO. That is, the angle between the proximal section portions decreases asthe depth of the curve C1 within the ostium O increases. Knowledge ofthis depth provides an indication of the location of theablative/mapping elements 22, 24 relative to the ostium O.

Next, the localization subsystem 6 is operated in the “PassiveDeformation” and/or “Snap Deformation” mode and the curve C1 rotatedwithin the ostium O to place the catheter distal tip at various sitesaround the ostium O, thereby collecting points for which the graphicalprocessor 62 can use to graphically generate a representation of theostium O (shown in FIG. 16) within the graphical endocardial surfacerepresentation S.

Notably, if a steering mechanism is provided, the radius of curvature ofthe curve C1 can be decreased (FIG. 17F-1 and 17F-2), thereby preventingthe resiliency of the distal member 30 from causing the curve C1 to grabthe inner surface of the pulmonary vein PV as it is rotated. In theillustrated method, decreasing the radius of curvature of the curve C1deflects the medial section 42 towards the proximal end of the proximalsection 40 (in the direction of the arrow) a distance of about ½ inch tofully release the curve C1 from the inner surface of the pulmonary veinPV. The steering mechanism can also be operated to allow the resiliencyof the distal member 30 to passively increase the radius of curvature ofthe curve C1 (e.g., by removing the tension created by the steeringmechanism), so that the curve C1 reengages the inner surface of thepulmonary vein PV. In the case where the steering mechanism provides thesole means for deflecting the proximal section 40, the radius ofcurvature of the curve C1 can be actively increased via operation of thesteering mechanism. This iterative curve C1 decreasing, curve C1rotation, and curve C1 increasing technique can be used during mappingand ablation of the tissue adjacent the ostium O in order to place theablative/mapping elements 22/24 is firm contact with different tissuesites described below.

Once the graphical representation of the ostium O has been created, themapping processor 16 (shown in FIG. 1) is operated in order to obtainand record ECG signals from the ostium, with the ablative element 22serving as a mapping element to measure ECG signals outside of theostium O, and the mapping element 24 serving to measure ECG signalsinside of the ostium O. As described below, these ECG signals will becompared with the ECG signals obtained subsequent to an ablationprocedure in order to determine if the resultant lesion has successfullyelectrically isolated the arrhythmia causing substrates from the leftatrium LA of the heart H. Additional tissue sites can be mapped byrotating the curve C1 within the ostium O about the apex A1 to place theablation/mapping elements 22, 24 in contact with other tissue sites, andoperating the mapping processor 16.

Once the pre-ablation ECG signals have been obtained and recorded, theablative element 22 is placed in contact with a first tissue site S1(FIG. 17G). This can be accomplished simply by leaving the curve C1 inplace after mapping has been completed or by rotating the curve C1within the ostium O about the apex A1 to place the ablative element 22into contact with a different tissue site at which the last mappingprocedure was performed.

The RF generator 18 (shown in FIG. 1) is then operated in order toconvey RF energy to the ablative element 22 (either in the monopolar orbipolar mode), thereby creating a linear lesion L1 (FIG. 17H). As can beseen, the linear lesion L1 is tangential to the perimeter of the ostiumO, thereby maximizing the span of the lesion L1 about the ostium O andthe effectiveness of the lesion L1 in blocking the errant electricalpathways from the pulmonary vein PV. Alternatively, the linear lesion L1may be somewhat oblique to the perimeter of the ostium O, but preferablydoes not deviate more than 30 degrees from the tangent to the ostium O.

Next, the curve C1 is again rotated within the ostium O about the apexA1 to place the ablative element 22 into contact with a second tissuesite S2 (FIG. 17I). Then, the RF generator 18 is operated again in orderto convey RF energy to the ablative element 22, thereby creating anotherlinear lesion L2 (FIG. 17J). As can be seen, the linear lesion L2, likethe linear lesion L1, is tangential to the perimeter of the ostium O,thereby maximizing the span of the lesion L2 about the ostium O and theeffectiveness of the lesion L2 in blocking the errant electricalpathways from the pulmonary vein PV. In the illustrated method, thelocation of the second tissue site S2 is selected such that the linearlesions L1 and L2 form a continuous lesion. This ablation process isrepeated until the entire ostium O is encircled with a circumferentiallesion. Alternatively, if the locations of the arrhythmia causingsubstrates are known, the tissue sites S can be selected, such thatdiscrete linear lesions L are formed around the ostium O at strategiclocations.

As can be appreciated, formation of the lesions L around the ostium Ocan be more controlled and predefined, since movement of the ablativeelement 22 is limited to a circle having a point at the apex A1 of thecurve C1. This can be contrasted with the previous “free-hand” approachwhere movement of the ablative element 22 is unlimited and difficult tocontrol. In addition, the unique design of the distal member 30 ensuresthat the ablative element 22 is kept out of the PV where irreparabledamage can be caused.

After the lesion has been created, the mapping processor 16 is againoperated to obtain and record ECG signals from the PV. Thesepost-ablation ECG signals are compared to the pre-ablation ECG signalsto determine whether the circumferential lesion has completely isolatedthe arrhythmia causing substrates in the pulmonary vein PV from the LAof the heart H. Once proper ablation has been confirmed, the guidesheath 12 and ablation/mapping catheter 14 are removed from thepatient's body, or alternatively, are used to create a circumferentiallesion within another pulmonary vein.

Although particular embodiments of the present invention have been shownand described, it will be understood that it is not intended to limitthe present invention to the preferred embodiments, and it will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present invention as definedby the claims.

1. A catheter for performing a medical procedure on tissue adjacent anostium of an anatomical vessel, comprising: an elongated flexiblecatheter body including a proximal shaft portion and a distal shaftportion having a proximal section pre-shaped to form a curve having anapex sized to be inserted into an anatomical vessel, and a distalsection configured to contact tissue adjacent an ostium of the vesselwhen the curve apex is inserted within the vessel ostium; and a steeringmechanism configured for decreasing a radius of curvature of the curve.2. The catheter of claim 1, wherein the curve is eccentric and theradius of curvature is smallest at the curve apex.
 3. The catheter ofclaim 1, wherein the distal section is configured to be placed into anon-radial relationship with the vessel ostium when the curve apex isinserted into the vessel ostium.
 4. The catheter of claim 1, wherein thedistal shaft portion further has a medial section pre-shaped to formanother curve that bends in a direction opposite to the curve.
 5. Thecatheter of claim 4, wherein the curve is a simple curve, and the othercurve is a complex curve that bends in a direction opposite to andout-of-plane with the simple curve.
 6. The catheter of claim 1, whereinthe catheter comprises a therapeutic or diagnostic element carried bythe distal section.
 7. The catheter of claim 1, wherein the steeringmechanism is unidirectional.
 8. A method of performing a medicalprocedure adjacent an anatomical vessel using the catheter of claim 1,comprising: inserting the curve apex into an ostium of the vessel toplace the distal section in contact with a first tissue site adjacentthe vessel ostium; placing the proximal section in firm contact with aninner surface of the vessel; operating the steering mechanism todecrease the radius of curvature of the curve within the vessel, wherebythe proximal section is released from firm contact with the inner vesselsurface; and rotating the decreased curve within the vessel about thecurve apex to place the distal section in contact with a second tissuesite adjacent the vessel ostium.
 9. The method of claim 8, wherein thevessel has a size that is smaller than the size of the curve, such thatthe proximal section is placed in firm contact with the inner vesselsurface during insertion of the proximal section within the vesselostium.
 10. The method of claim 8, further comprising operating thesteering mechanism to allow the radius of curvature of the curve toincrease within the vessel, whereby the proximal section is placed infirm contact with the inner vessel surface again.
 11. A method ofperforming a medical procedure adjacent an anatomical vessel using acatheter having a proximal section and a distal section, comprising:forming the proximal section into a curve having an apex; inserting thecurve apex into an ostium of the vessel to place the distal section incontact with a first tissue site adjacent the vessel ostium; placing theproximal section in firm contact with an inner surface of the vessel;decreasing a radius of curvature of the curve within the vessel, wherebythe proximal section is released from firm contact with the inner vesselsurface; and rotating the decreased curve within the vessel about thecurve apex to place the distal section in contact with a second tissuesite adjacent the vessel ostium.
 12. The method of claim 11, wherein theproximal section is pre-shaped to form the curve in the absence of anexternal force.
 13. The method of claim 11, wherein a steering mechanismis operated to decrease the radius of curvature.
 14. The method of claim11, wherein the vessel has a size that is smaller than the size of thecurve, such that the proximal section is placed in firm contact with theinner vessel surface during insertion of the proximal section within thevessel ostium.
 15. The method of claim 8, further comprising operatingthe steering mechanism to allow the radius of curvature of the curve toincrease within the vessel, whereby the proximal section is placed infirm contact with the inner vessel surface again.
 16. The method ofclaim 8, wherein the distal section is placed into a non-radialrelationship with the vessel ostium when the curve apex is inserted intothe vessel ostium.
 17. The method of claim 8, wherein the distal shaftportion further has a medial section, the method further comprisingforming the medial section into another curve that bends in a directionopposite the curve.
 18. The method of claim 17, wherein the curve is asimple curve, and the other curve is a complex curve that bends in adirection opposite to and out-of-plane with the simple curve.
 19. Themethod of claim 8, wherein the vessel is a pulmonary vein.
 20. A methodof performing a medical procedure adjacent an anatomical vessel using acatheter including a catheter body having a proximal section and adistal section, and at least one operative element carried by the distalsection, comprising: forming the proximal section into a curve having anapex; inserting the curve apex into the vessel ostium to place theoperative element in contact with a first tissue site of an ostium ofthe vessel; placing the proximal section in firm contact with an innersurface of the vessel; operating the at least one operative element atthe first tissue site; decreasing a radius of curvature of the curvewithin the vessel, whereby the proximal section is released from firmcontact with the inner vessel surface; rotating the decreased curvewithin the vessel about the curve apex to place the at least oneoperative element in contact with a second tissue site adjacent thevessel ostium; increasing the radius of curvature of the curve withinthe vessel, whereby the proximal section is placed in firm contact withthe inner vessel surface again; and operating the at least one operativeelement at the second tissue site.
 21. The method of claim 20, whereinthe proximal section is pre-shaped to form the curve in the absence ofan external force.
 22. The method of claim 20, wherein a steeringmechanism is operated to decrease the radius of curvature.
 23. Themethod of claim 20, wherein the vessel has a size that is smaller thanthe size of the curve, such that the proximal section is placed in firmcontact with the inner vessel surface.
 24. The method of claim 20,further comprising operating the steering mechanism to allow the radiusof curvature of the curve to increase within the vessel, whereby theproximal section is placed in firm contact with the inner vessel surfaceagain.
 25. The method of claim 20, wherein the distal section is placedinto a non-radial relationship with the vessel ostium when the curveapex is inserted into the vessel ostium.
 26. The method of claim 20,wherein the distal shaft portion further has a medial section, themethod further comprising forming the medial section into another curvethat bends in a direction opposite the curve.
 27. The method of claim26, wherein the curve is a simple curve, and the other curve is acomplex curve that bends in a direction opposite to and out-of-planewith the simple curve.
 28. The method of claim 20, wherein the at leastone operative element comprises a tissue ablative element, and theoperation of the at least one operative element comprises deliveringablation energy to the ablative element to create lesions at therespective first and second tissue sites.
 29. The method of claim 20,wherein the at least one operative element comprises a tissue mappingelement, and operation of the mapping element comprises receivingmapping signals from the mapping element to create mapping data pointsat the first and second tissue sites.
 30. The method of claim 20,wherein the vessel is a pulmonary vein.